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Prefreezing Post-thawing
Bull motility motility Survival
(percent) (percent) (percent)
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1 50 40 80
2 40 13 32
3 60 15 25
4 30 15 50
5+6 40 25 62
Average 44 22 50
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To determine whether epididymal sperm would withstand freezing, the 12
epididymides (cauda only) of 6 slaughtered bulls were flushed with
saline (0.9 percent) and the sperm obtained were frozen using the same
procedure as was used with the 20 consecutive ejaculates discussed
earlier. Averages of the 2 epididymides from each bull are given in
Table 3; the samples from bulls 5 and 6 were combined. From the data in
Table 3, it is obvious that motile sperm were present after freezing and
thawing epididymal samples. It is likely that further experience in
handling epididymal sperm may lead to improved results. Using frozen
epididymal sperm from 2 bulls, Canadian workers have produced confirmed
pregnancies in 8 out of 12 cows.[8]
=Freezability of washed sperm.= In the laboratory it is frequently
desirable to study sperm free of the seminal plasma in which they are
ejaculated. Sperm can be separated from the seminal plasma by
centrifugation, removal of the supernatant plasma, and resuspension in a
salt solution of known composition. Sometimes it is desirable to repeat
the process. This tends to wash the sperm with the salt solution and
sperm handled in this way are called washed sperm.
Sperm cells centrifuged three times and washed twice in 0.9 percent
sodium chloride solution withstood freezing well when finally
resuspended and frozen in yolk-citrate diluent. The percentage of
survival in three samples subjected to this treatment was 60 percent.
Thus it appears that the seminal plasma itself is not essential for
ejaculated sperm to survive the rigors of freezing. This is not
surprising, since it had already been found that epididymal sperm, which
also are free of accessory gland secretions, can withstand freezing and
thawing.